Testing To See If A Window Is Open

I am trying to check if my new window is open and if it is change the url.
This works until I use the x in the corner to close the window. At that
point i get an error when i try to open the window again. I believe that it
is because newWindow is still active. How do I close newWindow when it is
unloaded or closed by the x. If this is truely the problem.

function openWindow()
{
if (typeof (newWindow) == "undefined" || newWindow.open == false)
{
newWindow = window.open("http://www.yahoo.com","","width=400,height=400");
newWindow.focus();
return false;
}
else
{
newWindow.location.href = "http://www.msn.com"
}}

Here's my solution, seems a little redundant though.
function openWindow()
{
if (typeof (newWindow) == "undefined" || newWindow.open == false)
{
newWindow = window.open("http://www.yahoo.com","","width=400,height=400");
newWindow.focus();
return false;
}
else
{
newWindow.close()
newWindow = window.open("http://www.msn.com/","","width=400,height=400");
newWindow.focus();
return false;
}}